1. Field of the Invention
This invention relates generally to a scanner for scanning an object from a plurality of positions, and more particularly to a scanner used in a copying apparatus for scanning a document which may be set in a plurality of positions.
2. Description of the Related Art
A copying machine has an optical unit for forming a latent electrostatic image on a photosensitive drum which corresponds to an original document supported on a glass table. The optical unit includes a lens which focuses a light image of the document onto the drum to form the electrostatic image. The size of the copying machine is directly affected by the focal length of the lens so as the focal length of the lens increases, the size of the copy machine also increases. It is important, therefore, in the miniaturization of a copying machine that the focal length of the lens be made as short as possible.
Most copying machines have a glass table on which the document to be copied is supported. Typically, the size of the glass table is larger than the maximum size document (hereinafter referred to as the maximum copyable size) that the copying machine is able to copy. A reference mark for use in positioning documents for copying is typically located at the left side of the glass table. If a document of the maximum copyable size is set on the glass table at the left reference mark, a portion of the glass table is not covered by the document, i.e., a blank portion is present on the glass table. The optical unit moves within the range defined by the maximum copyable size document, but not in the blank portion.
It is desirable to use the blank portion for setting a document for copying. This would require that the optical unit move in the blank portion, which, in turn, would require that the focal length of the lens be increased. Increasing the focal length of the lens would then cause the size of the copying machine to be increased, which is undesirable.